1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for manufacturing the same. More particularly, the present invention relates to a method for manufacturing a pixel electrode of a liquid crystal display (LCD) device by irradiating portions of an amorphous indium tin oxide (ITO) deposited on a passivation layer with light (e.g., an excimer laser beam, UV light, etc.) to selectively form crystalline (or polycrystalline) indium tin oxide and selectively etching the uncrystallized portions of amorphous indium tin oxide.
2. Discussion of the Related Art
Owing to their small size, reduced thickness and weight, ability to display grayscales and moving pictures while consuming a minimal amount of power, liquid crystal display (LCD) devices are used as substitutes for cathode ray tubes (CRTs). LCD devices generally comprise an LCD panel made up of a thin film transistor (TFT) substrate and a color filter substrate separated from each other by a layer of liquid crystal material.
The thin film transistor (TFT) substrate supports a plurality of gate lines and data lines, crossing the gate lines. Thin film transistors (TFTs) are formed at crossings of the gate and data lines and pixel electrodes are formed in pixel regions defined by the plurality of gate and data lines. The color filter substrate supports a color filter layer and a common electrode. The layer of liquid crystal material may be interposed between the two substrates through an injection process. Electrodes are formed on surfaces of the TFT and the color filter substrates such that the surfaces of the two substrates supporting the electrodes face each other and contact molecules of the layer of liquid crystal material injected between the two substrates.
Images are displayed on the LCD panel by selectively controlling the light transmittance characteristics of the layer of liquid crystal material. Accordingly, electric fields, generated upon the application of a voltage to the electrodes on the two substrates, affect the orientation of molecules of the layer of liquid crystal material to control the light transmittance characteristics of the layer of liquid crystal material.
LCD devices known as active matrix LCD (AM-LCD) devices have are capable of displaying images at high resolutions as well as high quality moving images. AM-LCD devices include TFTs connected to pixel electrodes arranged in a matrix pattern on a lower substrate, a common electrode on an upper substrate, and a layer of liquid crystal material interposed between the upper and lower substrates. In AM-LCD devices, molecules of the layer of liquid crystal material are driven by electric fields present between the pixel and common electrodes and substantially perpendicular to the lower and upper substrates.
A related art LCD device will now be explained in greater detail.
FIG. 1A illustrates a schematic view of a related art LCD device and FIG. 1B illustrates a cross-sectional view of the related art LCD device of FIG. 1A taken along line I-I′.
Referring to FIG. 1A, the related art LCD device includes a plurality of gate lines 1 and data lines 3 formed to cross each other and to define a plurality of pixel regions, a plurality of pixel electrodes 8 formed in respective ones of the pixel regions, and a plurality of thin film transistors 7 formed at crossings of the gate and data lines 1 and 3 capable of applying video signals from the data lines 3 to corresponding pixel electrodes 8 in response to signals from the gate lines 1. The gate and data lines 1 and 3 are made of a semitransparent material such as an aluminum metal compound having a low resistance while the pixel electrodes 8 are made of a transparent material such as indium tin oxide (ITO).
Referring to FIG. 1B, the gate line 1 is formed along a first direction on a first substrate 9 and includes a gate electrode 2 protruding from the gate line 1. Next, a gate insulating layer 11 is formed over the entire surface of the first substrate 1 and on the gate line 1. Next, an island-shaped semiconductor layer 12 is formed on the gate insulating layer 11 in a region above the gate electrode 2. The data line 3 is formed on the gate insulating layer 11 along a second direction, substantially perpendicular to the first direction. A source electrode 5a is formed to protrude from the data line 3 and extend over a first side of the semiconductor layer 12 while a drain electrode 5b is formed to extend over a second side of the semiconductor layer 12, opposite the first side, and spaced apart from the source electrode 5a by a predetermined distance. Accordingly, a thin film transistor (TFT) 7 is formed where each of the gate and data lines 1 and 3 cross each other.
Subsequently, a passivation layer 13 is formed over the entire surface of the first substrate 9 and on the thin film transistor 7. Further, a contact hole is formed in a portion of the passivation layer over the drain electrode 5b. The pixel electrode 8 is then formed on the passivation layer 13 in the pixel region and is electrically connected to the drain electrode 5b through the contact hole. Next, a first alignment layer 17a, capable of regularly orienting liquid crystal molecules, is formed over the entire surface of the first substrate 9 and on the pixel electrode 8 and passivation layer 13.
Still referring to FIG. 1B, a second substrate 10 supports a black matrix layer 14 for preventing light leakage in regions outside the pixel region of the first substrate 9 (i.e., regions corresponding to the gate line 1, the data line 3, and the thin film transistor 7), Red/Green/Blue (R/G/B) color filter layers 15 for selectively transmitting light having predetermined wavelengths formed within each pixel region, a common electrode 16 having a potential different from that of the pixel electrode 8, and a second alignment layer 17b, capable of regularly orienting liquid crystal molecules, formed over the common electrode 16.
Subsequently, spacers (not shown) and sealant material (not shown) are formed between the first and second substrates 9 and 10, to bond the first and second substrates 9 and 10 together and to uniformly separate the bonded substrates by predetermined distance. Finally, liquid crystal material is injected between the bonded substrates 9 and 10 to form a layer of liquid crystal material 23.
Techniques used in manufacturing the aforementioned LCD device are similar to those used in manufacturing silicon semiconductors. For example both techniques involve thin film deposition process steps and process steps involving the photolithographic patterning of the thin film (e.g., photoresist (PR) deposition, ultraviolet (UV) exposure and developing, etching, and PR strip and cleaning process steps). Accordingly, the aforementioned method of manufacturing LCD devices requires repetitive process steps to form thin films.
FIGS. 2A to 2F illustrate cross-sectional views of process steps required to manufacture the related art LCD device.
Referring first to FIG. 2A, to manufacture the related art LCD devices, a metal layer is deposited on a first substrate 9 and patterned so as to form a gate line 1 and gate electrode 2. Next, a gate insulating layer 11 is deposited over the entire surface of the first substrate 9. Next, the semiconductor layer 12 is deposited over the entire surface of the first substrate 9 and is selectively removed, leaving an island-shaped semiconductor layer 12 above the gate electrode 2, wherein the island-shaped semiconductor layer 12 constitutes the active layer of the thin film transistor (TFT).
Subsequently, a metal layer is deposited over the entire surface of the first substrate 9 and patterned so as to form a data line 3 and source/drain electrodes 5a and 5b, respectively. A passivation layer 13 is formed over the entire surface of the first substrate 9 and on the data line 3. Next, a portion of the passivation layer 13 is selectively removed to form a contact hole exposing the drain electrode 5b. An amorphous indium tin oxide film (a-ITO) is then deposited on the passivation layer 13 in a low temperature sputtering process such that the a-ITO film electrically contacts the drain electrode 5b through the contact hole.
Referring to FIG. 2B, a photoresist layer 20 is deposited on the a-ITO film 8a and is subsequently hardened in a baking process.
Referring to FIG. 2C, a mask 21 is positioned above the photoresist layer 20. Regions of the photoresist layer 20 not directly underlying the mask 21 are then exposed to ultraviolet rays 22.
Referring to FIG. 2D, portions of the photoresist layer 20 that were exposed to the UV light are removed in a developing process.
Referring to FIG. 2E, portions of the a-ITO film 8a, exposed upon the removal of portions of the photoresist layer 20, are etched using an etchant wherein the remaining portions of the photoresist layer 20 act as an etch mask. Generally, etchants such as diluted oxalic acid or diluted hydrochloric acid are used to etch a-ITO films.
Referring to FIG. 2F, the remaining photoresist layer 20 is stripped, the substrate is cleaned, and a pixel electrode 8 is thus formed.
The related art method described above forms the pixel electrode 8 by patterning an amorphous indium tin oxide film deposited on a passivation layer via conventional photolithography and etching processes. Accordingly, the related art method described above is disadvantageous because forming pixel electrodes via conventional photolithography processes (e.g., depositing photoresist layer on the amorphous indium tin oxide thin film, exposing the photoresist layer, developing the photoresist layer, etching the amorphous indium tin oxide thin film using the photoresist layer as an etch mask, stripping the photoresist layer, and cleaning the substrate) increases the risk of generating defects and decreases the yield due to the application of complicated and time consuming photolithographic steps. Further, the monetary expense and time required to install and maintain photolithographic equipment and consistent patterning procedures can be prohibitively excessive.